: The successful demonstration of (Si)Ge1-xSnx alloys as direct-gap materials for infrared lasers has driven intense research on group IV-based devices for nanoelectronics, energy harvesting, and quantum computing applications. The material palette of direct-gap group-IV alloys can be further extended by introducing carbon to fine-tune their structural and electronic properties, significantly expanding their functionality. This work presents heteroepitaxial growth of C(Si)GeSn alloys using an industry-standard reduced-pressure chemical vapor deposition reactor. The introduction of CBr4 as a precursor enables controlled incorporation of C atoms (<1 at.%) into the epilayer lattice, while simultaneously increasing the Sn content in the CGeSn alloy up to ≈18 at.%. Carbon plays a key role in modulating strain, stabilizing the crystal structure, and influencing material properties. By leveraging alloying and strain engineering, quaternary CSiGeSn bulk layers and CGeSn/GeSn heterostructures are epitaxially grown. The impact of C incorporation on optical emission is investigated in LEDs based on CGeSn/GeSn multiple quantum wells, demonstrating enhanced near-infrared emission at 2.54 μm, which is sustained up to room temperature
